1. Field of the Invention
The invention relates generally to the design of running strings and power arrangements for downhole electrically operated tools, such as electric submersible pumps.
2. Description of the Related Art
A large number of downhole electrically operated devices are used during drilling of a wellbore and subsequent production of hydrocarbons. These electrically operated devices include electric submersible pumps (ESPs) as well as a variety of electric sensors, electric heaters and electric motors.
Running strings are used to disposed downhole electrically operated devices into a wellbore. Presently, running strings can either be made up of interconnected sections of conventional oil field tubular members or be coiled tubing. Coiled tubing running strings have become a popular form of running string to run an ESP or other electrically operated devices into a wellbore. In part, this is because they permit an ESP to be installed and retrieved in a live well and obviate the need for a workover rig. The ESP is supplied operating power from surface via a power cable. In conventional systems, the power cable is either retained within the flowbore of the running string or clamped to the outer radial surface of the running string. Even where the power cable is armored, it presents a potential failure point for an ESP arrangement due to wellbore debris and corrosion.